Field of the Invention
The present invention relates to a driver device for a display panel which has pixel cells, serving as pixels, arranged on respective display lines of the display panel.
Recently, where two-dimensional image display panels are concerned, plasma display panels (hereinafter called ‘PDP’), in which a plurality of discharge cells are arranged in the form of a matrix, have been attracting attention. The subfield method is known as a driving method for displaying an image corresponding with a video input signal on the PDP. The subfield method divides a single-field display period into a plurality of subfields and causes each of the discharge cells to selectively discharge light in each subfield in accordance with the luminance level represented by the video input signal. Accordingly, an intermediate or grayscale luminance corresponding with the total light emission period within the single-field period is then perceived.
FIG. 1 of the attached drawings shows an example of a light emission drive sequence based on this subfield method. This emission drive sequence is disclosed in, for example, Japanese Patent Application Kokai (Laid-Open Publication) No. 2000-227778.
The light emission drive sequence shown in FIG. 1 divides a single field period into 14 subfields, which are the subfields SF1 to SF14. All the discharge cells of the PDP are initialized in lit mode only in the leading subfield SF1 of these subfields SF1 to SF14 (Rc). Each of the subfields SF1 to SF14 sets some of the discharge cells to unlit mode in accordance with the video input signal (Wc) and causes only the discharge cells of lit mode to discharge light over the period allocated to the subfield concerned (Ic).
FIG. 2 of the attached drawings shows an example of a light emission drive pattern in a single field period of each discharge cell that is driven on the basis of this light emission drive sequence (see Japanese Patent Application Kokai No. 2000-2277785).
According to the light emission pattern shown in FIG. 2, the discharge cells initialized in lit mode in the leading subfield SF1 are then set to unlit mode in a particular one subfield of the subfields SF1 to SF14, as indicated by the black circles. Once the discharge cell is set to unlit mode, the discharge cell does not re-enter lit mode until the one field period ends. Accordingly, during the period until the discharge cells are set to unlit mode, as indicated by the white circles, the discharge cells discharge light continuously in these subfields. Here, each of the fifteen different light emission patterns shown in FIG. 2 has a different total light emission period within a single field period, and hence fifteen different intermediate luminances are rendered. That is, an intermediate luminance display for (N+1) grayscales (N being the number of subfields) is feasible.
However, with this driving method, because there are restrictions on the number of subfields, there is a shortage in the number of grayscales. In order to compensate for the shortage in the number of grayscales, multiple gtayscale processing such as error diffusion and dither processing is performed on the video input signal.
Error diffusion processing converts the video input signal into 8-bit pixel data, for example, for each pixel. The upper 6 bits of the pixel data is treated as display data and the remaining lower two bits of the pixel data is treated as error data. Then, the error data of the pixel data are weighted and added based on the respective peripheral pixels and the resultant is reflected in the display data. As a result of this operation, a pseudo-representation of the luminance of the lower two bits of the original pixel is provided by the peripheral pixels, and, consequently, a luminance grayscale representation of the 8 bits of pixel data is possible by means of the six bits of display data. Further, dither processing is performed on the six-bit error-diffusion-processed pixel data obtained by the error diffusion processing. In dither processing, a single pixel unit is rendered from a plurality of adjoining pixels, and dither coefficients consisting of different coefficient values are allocated and added to the error-diffusion-processed pixel data corresponding with the respective pixels in the single pixel unit. As a result of the addition of the dither coefficients, when viewed in the single pixel unit, the luminance of the 8-bit original data can be represented by only the upper four bits of the dither-added pixel data. Therefore, the upper four bits of the dither-added pixel data are extracted and allocated to each of the 15 different light emission patterns shown in FIG. 2 as multiple grayscale pixel data PDs.
However, in the case of a four row by four column dither pattern (when sixteen dither coefficients are used), for example, the dither pattern must be repeated in sixteen-field cycles in order to express all the luminance as viewed in a single pixel unit. Therefore, when multiple grayscale processing is to be performed by means of multiple bit-number compression, the recursive cycle becomes long. This means that the observed integration effect cannot be expected and the picture quality deteriorates.